Side Determination of the Tibia and Fibula: A Step-by-Step Method

After the femur, the tibia and fibula are the lower limb bones most often handed over in an osteology viva. The tibia is easy once you know where to look. The fibula is the one students get wrong, because its two ends look alike at first glance. Both yield to the same three questions used for side determination of the femur and humerus.

The three questions

1. Which end is the upper end?
2. Which surface faces forwards?
3. Which side is medial?

Settle them in that order. Then hold the bone against your own leg in that position. The leg it matches is its side.

First, which bone is which?

The tibia is the thick, medial bone of the leg: the shin bone. It carries the body weight from the knee to the ankle. The fibula is the thin, lateral bone. It takes no part in the knee joint, but its lower end forms the outer side of the ankle.

Side determination of the tibia

• Upper end: the broad, expanded end with two condyles and a flat top. The lower end is much smaller.
• Front: the tibial tuberosity is on the front of the upper end. Below it, the sharp anterior border, the shin, runs down the front of the shaft. The back of the shaft carries the oblique soleal line.
• Medial: the medial malleolus projects downwards from the medial side of the lower end. The lateral side of the lower end has the fibular notch, where the fibula fits.

Putting it together: hold the tibia with the broad end at the top and the tibial tuberosity facing forwards, away from you. The side on which the medial malleolus hangs down is the medial side. If the malleolus is on your left, it is a right tibia. If it is on your right, it is a left tibia.

Second check: the medial surface of the shaft is smooth and lies just under the skin; you can feel it along your own shin. The lateral side of the shaft has the interosseous border, which faces the fibula.

Anatomical position: hold the tibia vertically, with the tuberosity in front and the medial malleolus pointing down and medial.

Side determination of the fibula

Start with the ends, and take your time. Most mistakes happen here.

• Upper end (head): slightly expanded in all directions, like a small knob. It has a round facet on top for the tibia, and a pointed styloid process (the apex) projecting upwards.
• Lower end (lateral malleolus): flattened from side to side and longer from front to back. Its medial surface has a triangular articular facet for the talus.
• Front and back: at the lower end, the triangular facet is in front and a deep pit, the malleolar fossa, lies behind it.
• Medial: the triangular facet and the malleolar fossa are both on the medial surface of the lower end. The lateral surface of the malleolus is smooth and lies under the skin.

Putting it together: hold the fibula with the flattened end at the bottom. Turn it until the malleolar fossa is at the back, behind the triangular facet. The surface that carries the facet and the fossa now faces medially, towards the tibia. If that surface faces your left, with the front of the bone facing away from you, it is a right fibula. If it faces your right, it is a left fibula.

One line to remember: on the fibula, the malleolar fossa is medial and behind.

Tibia and fibula side by side

Common mistakes

• Holding the fibula upside down. Check for the flattened malleolus and its fossa before anything else.
• Using the tibial tuberosity alone. It tells you front and top, not the side. You still need the medial malleolus.
• Deciding the side before fixing front and back. Always settle upper end, then front, then medial.
• Answering from one feature. Confirm with a second landmark before you speak.

Questions students ask

How do I quickly tell a left tibia from a right tibia?

Put the broad end up and the tibial tuberosity in front. The medial malleolus is on the inner side. On a right tibia held this way, with the front facing away from you, the malleolus is on your left.

Which is the upper end of the fibula?

The head: the end that is expanded in all directions and carries the styloid process. The lower end is flattened from side to side and has the malleolar fossa.

Why is the side of the fibula harder to determine than the tibia?

The fibula is slender and its two ends are similar in size, so it is easy to turn upside down. The tibia has an obviously broad upper end and a single malleolus, so its position is clear at once.

Which malleolus is lower, medial or lateral?

The lateral malleolus, on the fibula, reaches lower than the medial malleolus of the tibia. You can feel this at your own ankle.

Is the tibia medial or lateral to the fibula?

The tibia is medial. The fibula is lateral.

What does the examiner ask after side determination?

Usually the anatomical position, then the named features: on the tibia, the condyles, tibial tuberosity, soleal line and medial malleolus; on the fibula, the head, styloid process, lateral malleolus and malleolar fossa. See how to identify any bone in a spotter for the full routine.

Practise it

Side determination becomes quick only with a bone in your hand. A bilateral bone set gives you a left and a right tibia and fibula to compare; a unilateral bone set is enough to practise the method. The XBONZ Anatomy Lab has a side-determination drill on the 3D skeleton, with full access. For a study plan, read how to study osteology in first year.

This is a revision aid. Check it against your course textbook and what your department teaches.